Device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation

ABSTRACT

The invention relates to a device for the storage of at least one photomask for lithographic projection and a method for using the device in an exposure installation. A container is suitable for receiving a photomask. The container has a housing, a closable opening device situated at the container housing and serving for the entry and issuing of the photomask, and one gas inlet opening arranged to purge the photomask. The invention also relates to a method for using the device in an exposure installation.

This application claims priority to German Patent Application 10 2005061 571.6, which was filed Dec. 22, 2005 and is incorporated herein byreference.

TECHNICAL FIELD

The invention relates to a device for the storage and use of at leastone photomask for lithographic projection and a method for using thedevice in an exposure installation.

BACKGROUND

For the production of integrated circuits, layers provided withdifferent electrical properties are usually applied on semiconductorwafers and patterned lithographically in each case. A lithographicpatterning step usually consists in applying a photosensitive resist,exposing the latter with a desired structure for the relevant plane anddeveloping it, and subsequently transferring the resultant resist maskinto the underlying layer in an etching step or using the resist mask asan implantation mask for altering the electrical properties of theunderlying layer in a targeted manner.

For the lithographic projection step of a circuit pattern, a waferscanner or wafer stepper is usually used as exposure apparatus. In theexposure apparatus, the photosensitive resist layer is exposed withelectromagnetic radiation having a predetermined wavelength, which, inpresent-day exposure technologies, lies for example in the UV or DUVrange at 256 nm, 193 nm or 157 nm. The exposure dose present during theexposure of the photosensitive resist layer at the location of thesemiconductor wafer is chosen according to the specifications of theresist layer.

Each individual layer of the circuit pattern is usually transferred tothe semiconductor wafer by means of a photomask. The photomask comprisesa transparent substrate layer provided with absorbent elements, such as,e.g., a chromium layer, which simulate the circuit pattern. Thephotomask, also called a reticle, is often provided with a protectivefilm (pellicle). The protective film serves to protect the structureside of the transparent substrate layer from deposits. Deposits on theprotective film itself are not normally transferred to the resist layerduring lithography since the protective film lies outside the focalrange for imaging onto the resist layer.

In large-volume fabrication processes, diverse attempts are made tooptimize the productivity. Besides the miniaturization of structuredimensions on the semiconductor wafers and the provision of processinstallations for semiconductor wafers having a diameter of 300 mm, atime-saving handling of the semiconductor wafers and photomasks in theprocess installations is also an important optimization variable.

In order to be able to use process installations from differentmanufacturers or of different types, standardized equipment is typicallyused. Thus, by way of example, the standardization committee “SEMI”standardizes a multiplicity of equipment for the semiconductor industrywith regard to the interoperability thereof.

SEMI Standard 111-0304 defines the configuration of reticle containerswhich are fed to the lithographic projection installations via a definedinterface. Reticle containers which satisfy said standard are usuallyreferred to as reticle SMIF pod (SMIF=standard mechanical interface) orby the abbreviation “RSP”, the purpose of which is to enable thereticles to be stored and transported within wafer fabrication. Reticlecontainers in accordance with said standard have a housing and a platewhich is arranged at the bottom of the housing and which can beautomatically closed or opened by the lithographic projectioninstallations or reticle inspection systems. In this case, RSPscomprising one reticle and also RSPs comprising six reticles are used asstorage containers.

In the case of the photomasks used in lithographic exposure processes,particles or contaminations can attach to the surface by adhesion fromthe surrounding atmosphere. Thus, by way of example, the presence ofammonium ions and/or sulfate ions on the reticle surface leads to theformation of ammonium sulfate ((NH₄)₂SO₄) or to the formation ofammonium oxalate ((NH₄)₂C₂O₄H₂O). These crystals can grow with energybeing radiated in by the light source of the exposure apparatus.

An example of crystal growth and irradiation with UV light is describedbelow. Air normally contains hydrogen sulfide (H₂S) in a lowconcentration. Together with oxygen, sulfur dioxide forms in accordancewith the reaction equation:2H₂S+3O₂−>2SO₂+2H₂O.  [1]

With light being radiated in during the lithographic projection, freeoxygen radicals are formed which react with sulfur dioxide in accordancewith the following reaction equation:SO₂+O−>SO₃  [2]

Together with (residual) water from the air, aerosol particles arise,which are chemically stable, in accordance with the following reactionequation:SO₃+H₂O−>H₂SO₄  [3]

In the presence of impurities, in this case ammonia, said aerosolparticles react to form ammonium sulfate, in accordance with thefollowing reaction equation:H₂SO₄+2NH₃−>(NH₄)₂SO₄  [4]

Photomasks in exposure apparatuses having exposure wavelengths in theDUV range exhibit a growth of said crystals which takes place virtuallylike an avalanche. Consequently, the photomasks have to be regularlymonitored and cleaned.

This cleaning is usually carried out at the mask company by themanufacturer of the photomasks. For cleaning purposes, the photomasksare introduced into an acid bath. By way of example, a solutioncontaining sulfuric acid is used as the acid bath. However, it has beenfound that the surface of freshly cleaned photomasks is still relativelysusceptible to crystal growth.

In addition to the productivity stoppage and the high costs due to thecleaning, it can also occasionally happen that a photomask is destroyedor damaged during cleaning. Furthermore, by way of example, phaseshifter masks can only be cleaned a few times since the properties ofthe phase shifters can change.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a device for thestorage and use of at least one photomask for lithographic projection isprovided, which comprises a container suitable for receiving aphotomask. The container includes a container housing and a closableopening device situated at the container housing and serving for theentry and issuing of the photomask. The container has at least one gasinlet opening arranged in such a way that, in the case of purging thephotomask, a purge gas flushes around the photomask with a laminar flow.

According to this embodiment of the invention, impurities directly inthe vicinity of the photomask in the volume over the transparentsubstrate are removed by means of the chemically active gases or gasmixtures, thereby suppressing crystal growth on the surface of thephotomask. Consequently, the photomask can be used significantly longerin a lithographic exposure process without suffering from the depositingof particles.

According to a further embodiment of the present invention of a methodfor using the device is provided. A fabrication installation includes atleast one exposure apparatus suitable for receiving the photomask. Thephotomask is fed from the container into the exposure apparatus. One ormore exposure processes are carried out with the exposure apparatususing light from a UV source. The photomask is removed from the exposureapparatus into the protective container and the photomask is cleaned inthe container by purging with the purge gas.

In a further embodiment, the following steps are furthermore performed.A microwave source is provided. The photomask is irradiated withmicrowave radiation. The photomask is cleaned in the container bypurging with the purge gas.

In a further embodiment, the following steps are furthermore performed.An infrared source is provided. The photomask is irradiated withinfrared radiation and the photomask is cleaned in the container bypurging with the purge gas.

In accordance with one embodiment of the invention, the device is usedin an exposure apparatus which can be operated with conventional loadingand unloading stations and also storage containers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail with reference to theaccompanying drawings:

FIG. 1 schematically shows a cross-sectional view through a device forthe storage of a photomask in accordance with one embodiment of theinvention;

FIG. 2 schematically shows a further cross-sectional view through adevice for the storage of a photomask in accordance with one embodimentof the invention;

FIG. 3 schematically shows a further cross-sectional view through adevice for the storage of a photomask in accordance with one embodimentof the invention;

FIG. 4 shows a perspective view of a mount in accordance with oneembodiment of the invention;

FIG. 5 shows a further perspective view of the mount according to FIG. 4with a device in accordance with one embodiment of the invention;

FIG. 6 schematically shows a further perspective view of a device inaccordance with one embodiment of the invention;

FIG. 7A schematically shows a further perspective view of a device inaccordance with one embodiment of the invention;

FIG. 7B schematically shows a further perspective view of a device inaccordance with one embodiment of the invention;

FIG. 8A schematically shows a further cross-sectional view through adevice in accordance with one embodiment of the invention;

FIG. 8B schematically shows a further cross-sectional view through adevice in accordance with one embodiment of the invention;

FIG. 9 shows a chemical structural formula of an impurity forillustrating the procedure according to the invention;

FIG. 10 shows an absorption spectrum in the infrared range of animpurity for illustrating the procedure according to the invention; and

FIG. 11 shows a transmission spectrum in the infrared range of aprotective film for illustrating the procedure according to theinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The invention is explained below in the context of the lithographicpatterning of semiconductor wafers, which is carried out, for example,during the fabrication of microelectronic circuits. It is appreciated,however, that the present invention provides many applicable inventiveconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to apply the method and to apply the device of the invention, anddo not limit the scope of the invention. Accordingly, the invention canbe applied in a multiplicity of production technologies in which apatterning step is effected by means of a photomask, thus, for example,during the production of thin-film components, such as, e.g., TFTelements, or else in nanotechnology.

FIG. 1 schematically shows a cross-sectional view through a photomaskfor lithographic projection in accordance with a first embodiment of theinvention. The photomask 5 has a transparent substrate 10, whichcomprises quartz, by way of example. On the front side 12, thetransparent substrate 10 is provided with a pattern 14 of structureelements 16. In this case, the pattern 14 corresponds to a level of acircuit design and is usually produced by means of a suitable CADprogram.

Depending on the type of mask, the structure elements 16 are embodied inabsorbent, partly absorbent or phase-shifting fashion. The mixture ofthese properties of the structure elements 16 is likewise possible.Absorbent structure elements 16 usually comprise chromium or blackchromium. A thinned chromium or molybdenum silicide is used for partlyabsorbent structure elements 16. The phase-shifting properties of thestructure elements 16 may be achieved for example by the use ofmolybdenum silicide or by an etch into the mask substrate 10 in order toform trench-like structure elements. It is, of course, also possible touse reflective mask types such as are used in EUV lithography by way ofexample.

As is shown in FIG. 1, the photomask 5 has a frame 18 arranged on thefront side 12 of the transparent substrate 10 outside the pattern 14 ofstructure elements 16. The frame 18 is usually embodied in rectangularor trapezoidal fashion in a plan view. The frame 18 is adhesively bondedonto the transparent substrate 10 and encloses the structure elements 16of the pattern 14.

A protective film 20, also called pellicle, is furthermore fixed on theframe 18, for example by adhesive bonding, above the transparentsubstrate 10. Said protective film 20, together with the front side 12of the transparent substrate 10 and the side walls of the frame 18,forms an at least spatially closed-off volume 26.

The protective film 20 is permeable to gaseous substances of the purgegas toward the volume 26. For this purpose, the protective film 20 maybe provided with a pinhole, for example, in order to enable a gasexchange between the volume 26 and the region outside the volume 26.Other openings or cutouts are likewise conceivable.

The device according to the invention furthermore has a container 30.The container 30 has a container housing 32 and a bottom flap 34situated at the container housing 32 as a closeable opening. Otheropenings might be provided for example at the sidewalls of the container30. The container housing 32 has an electrostatically dissipatingcoating, whereby the use of ionizers or the like is obviated.

The bottom flap 34 is provided for the entry and issuing of thephotomask 5. Furthermore, the bottom flap 34 has a gas inlet opening 40and a gas outlet opening 42, for example in the form of circular holeswithin the bottom flap 34. In this case, the position of the gas inletopening 40 and of the gas outlet opening 42 within the bottom flap 34can be chosen freely.

The container 30 is embodied so as to be able to receive the photomask5. For this purpose, the container housing 32 is provided with a reticleholder 50 in order to hold the photomask 5 in a predetermined position.The reticle holder 50 may be embodied as a pin or clamp, for example,thereby preventing the photomask 5 from slipping in a lateral directionand upward within the container housing 32. Furthermore, the bottom flap34 has a reticle support 52 in order to hold the photomask 5 in apredetermined position. The reticle support 52 is intended to preventthe photomask 5 from slipping in the direction of the bottom flap 34within the container housing 32.

For simpler use of the device in accordance with FIG. 1 within anexposure installation, the container 30 is provided with a handlingflange 54 fitted to the top side of the container housing 32. Thehandling flange 54 serves for transferring the photomask 5 to anexposure apparatus by means of a mechanical interface.

As mentioned in the introduction, for time-saving handling withinsemiconductor fabrication installations, a standardization of theprocess equipment used is provided. In consequent fashion, the container30 and the bottom flap 34 are embodied in accordance with an industrystandard, for example according to the SEMI Standard. The mechanicalinterface likewise corresponds to an industry standard according to oneof the SEMI Standards. It goes without saying that it is likewiseconceivable to use standards appertaining to a different industrystandard or else proprietary, in-house specifications.

The device in accordance with this embodiment furthermore has a purgedevice 44. The purge device 44 serves to remove impurities by means ofthe purge gas in the volume 26. As mentioned in the introduction, saidimpurities are for example ammonia, carbon dioxide or elsesulfur-containing gases, such as, e.g., hydrogen sulfide or sulfurdioxide. Said impurities could cause crystallization on the photomask 5,which is prevented on account of the impurities being transported awayby means of the purge gases of the purge device 44.

For this purpose, as shown on FIG. 3, the purge device 44 has a gas feedline 46 connected to the gas inlet opening 40, and a gas discharge line48 connected to the gas outlet opening 42. The purge device 44 serves topurge the container 30 with a purge gas in order to preventcrystallization on the photomask 5.

Particular consideration is given in this case to the position of thegas inlet opening 40 and the gas outlet opening 42. In order to preventthe purge gas from flushing around the photomask 5 in a turbulent flow,the gas inlet opening 40 and the gas outlet opening 42 are arrangedoffset with respect to the photomask. This results in a flow that is aslaminar as possible. The precise position of the gas inlet opening 40and of the gas outlet opening 42 can also be determined by means of acomputer simulation.

As is shown in FIG. 2, the volume within the container 30 iscontaminated with impurities that are present in low concentration forexample as a result of outgassing from the protective film 20, thecontainer 30 or adhesives used. As mentioned in the introduction, saidimpurities grow under irradiation with UV light, with the result thatdeposits 24 in crystal form may arise on the photomask 5.

The purge device 44 is preferably embodied with a mixing device forpurging with a plurality of gases. For this purpose, a mixing devicecomprising a T-piece and a mixing valve may be provided in order toadmix the plurality of gases in a desired mixing ratio. Moreover, inaddition to the mixing ratios, the gas temperature and/or the gaspartial pressures of the purge gas can be controlled by means of thepurge device 44. The container 30 is shown together with the purgedevice 44 in FIG. 3.

A plurality of purge gases is appropriate for eliminating theimpurities. In accordance with reaction equations [1] to [4], crystalgrowth is prevented by removing ammonia or sulfur-containing gases.Generally, a gas mixture for cleaning organic contaminations or a gasmixture for cleaning inorganic contaminations may be fed as purge gas.The purge gas used may also be weakly chemically active, in which case,in particular, the protective film 20 should not be attacked by thepurge gas.

By way of example, a nitrogen-ozone gas mixture is provided for cleaningorganic contaminations; the cleaning of inorganic contaminations iseffected, e.g., by means of a nitrogen-argon gas mixture. It is likewiseconceivable to feed a nitrogen-hydrogen gas mixture, for example as a90% nitrogen and 10% hydrogen forming gas. A nitrogen-carbon dioxide gasmixture is likewise possible.

The impurities within the container are transported away efficiently onaccount of the purging with the above-mentioned purge gases, therebylengthening the interval between external cleaning steps in a maskcompany. As a result, the service life of the photomask is significantlylengthened, and corresponding cleaning costs are saved.

A further aspect is that water is a starting point for manycrystallization processes on the photomask 5. Therefore, provision ismade for choosing the purge gas such that water molecules are removedfrom the photomask 5. Water molecules often occur as a molecularmonolayer on the surface of the transparent substrate. By purging with adried air mixture, a so-called XDA gas (XDA=extremely dry air), fromwhich the water component has been removed to the greatest possibleextent, the partial pressure is shifted correspondingly, resulting inevaporation of the water on the surface of the photomask.

FIGS. 4 and 5 show how the above-described concept of purging thephotomask 5 in the container 30 can be applied to storage systems. Theaim is for the storage and repository system provided in the context ofindustry standards to be configured compatibly with the invention.

As is shown in FIG. 4, a holding frame 56 is provided, which is able toreceive the container 30. The positioning of the container 30 in theholding frame 56 is effected by means of the handling flange 54 in thiscase. For tracking and individualization of photomasks within afabrication installation, the container 30 has a barcode identificationor electronic identification. The holding frame 56 is provided with areader for read-out, which can be visualized by means of a display 62.It is likewise possible to transmit read-out results to a centralprocess control by means of a network connection (not shown in FIG. 4).

In order to be able to receive a multiplicity of different containers,the purge device 44, rather than being connected to the bottom flap 34directly, is now connected via an adapter plate 58 arranged below thebottom flap 34 of the container. In this case, the adapter plate 58 isintroduced into the holding frame 56. For this purpose, the holdingframe 56 has fixings 60 at its edge in order to fix the adapter plate58.

The adapter plate 58 is embodied in the holding frame 56 as a rackbottom on which the container 30 with the photomask 5 can be placed. Thefixings 60 are embodied in screwable fashion in order to enable theadapter plate 58 to be exchanged. The gas feed line 46 is shown as apart of the adapter plate in FIG. 4.

For receiving the container 30, a hinged mechanism 64 is provided in theholding frame 56, which mechanism secures the container 30. As shown inFIG. 4, the hinged mechanism 64 is embodied in the form of a clip 66that is fitted to the holding frame 56 in rotatable fashion and can bepivoted into a receiving position 59 and a holding position 59′ as shownin FIG. 5. A securing pin 68 in the holding frame 56 or else in theadapter plate 58 is provided in order to increase the alignmentaccuracy.

To summarize, the holding frame 56 is connected to the purge device 44,then, so that purging with the purge gases can be carried out during thestorage of photomasks. The combination of container 30 and holding frame56 may be embodied in a manner conforming to an industry standard inthis case, for example according to the SEMI standard.

This concept is extended below, with reference to FIG. 6, to a storagesystem 70 comprising a plurality of receptacle locations for containers30. FIG. 6 shows a storage system 70 comprising six holding frames 56each for receiving one container 30. The storage system 70 has aclosed-off region accommodating the purge device 44 as storage for a gassystem 72. The required gas mixing devices, T-pieces or mixing valvesare likewise accommodated in the storage for the gas system 72.

A further embodiment is described making reference now to FIG. 7A.Depending on the gas used for purging it is not permissible to blow thepurge gases into the atmosphere surrounding the container due to safetyand health regulations to be observed during operation and/or for costreasons as uncontrolled gas losses would increase the amount of purginggas required. Therefore, attention is drawn to the connection betweenthe gas system and the container.

In FIG. 7A, the gas inlet opening 40 and the gas feed line 46 areschematically depicted in a side view. According to this embodiment, thegas inlet opening is arranged on the closable opening device 34. Note,that the adapter plate 58 can also be inserted in-between the gas inletopening 40 and the gas feed line 46, as described with respect to FIG.4. Accordingly, the description given below would then apply to theconnection between the adapter plate 58 and the gas system 44.

Both, the gas inlet opening 40 and the gas feed line 46 can be arrangedas stubs having respective diameters adapted to house the gas inletopening 40 within the gas feed line 46 or vice versa.

In FIG. 7A, the gas inlet opening 40 is shown as a cylindrical stub witha substantially uniform diameter chosen such that the required gas flowcan be achieved. The gas feed line 46 is formed by a cylindrical stubhaving two different diameters so as to result in a step-likecross-section.

The upper part of the gas feed line 46 has a diameter larger than thesize of the cylindrical stub of gas inlet opening 40. Accordingly, thegas inlet opening 40 and the gas feed line 46 can be put together in anoverlapping manner. It should be noted that many different shapes andcross-sections of the gas inlet opening 40 and the gas feed line 46 canbe used, including but not limited to elliptical or rectangular shapedstructures having conical, partially conical or multi-stepcross-sections.

In order to prevent gas from leaking at the joint between the gas inletopening 40 and the gas feed line 46, a gasket 36 is introducedin-between. As shown in FIG. 7A, the gasket is arranged in the lowerpart of the gas inlet opening 40 facing the gas feed lines where gasinlet opening 40 and the gas feed line 46 overlap with respect to eachother.

The gasket 36 can be of toroidal or ring-like shape as depicted in FIG.7A, other shapes are conceivable as well. The gasket 36 seals the regionbetween the gas inlet opening 40 and the gas feed line 46. In addition,the gasket 36 can provide a clamping function in order to retain thecontainer 30 to the gas system 44.

In order to achieve easily disassembling of the container 30 to the gassystem 44, the gasket can be provided as a collapsible gasket having apassive state of being either collapsed or expanded. By applying outsidepressure, the state of the collapsible gasket can be selected.

As an example, self inflatable synthetics can be used which seal the gasinlet opening 40 and the gas feed line 46 while inflated. Beforeremoving the container 30 from the gas system 44, extraction by suctionor by applying a vacuum collapses gasket. During purging of gases, noaction has to be taken, as the self inflatable gasket provides a sealand clamps the gas inlet opening 40 and the gas feed line 46.

In another conceivable arrangement of the gasket is shown in FIG. 7B.According to this embodiment, the gas inlet opening 40 is again formedas a cylindrical shaped stub protruding from the closable opening device34. The gas feed line 46 is formed in a cup-shaped manner so as to allowintroduction of the gas inlet opening 40 as depicted in FIG. 7B.

The gasket 36 is arranged as a sleeve having a double-walledcross-section. The double-walled cross-section results in an inner wallmember 37 and an outer wall member 38 joined at cusp 39. As shown inFIG. 7B, the outer wall member 38 of gasket 36 is attached to the gasfeed line 46, for example by gluing. It is, however, also conceivable toattach the gasket with the inner wall member or at the gas inlet opening40. The gasket 36 is inserted such that the cusp 39 faces the container30.

Generally speaking, the cusp 39 should point in the same direction withrespect to the gas flow purged through the gas feed line 46. Thisresults in a self-controlled sealing while purging gas through the gasinlet opening 40. As the incoming gas flow presses against the innerwall member 37 and outer wall member 38, a force results which tends toopen the inner wall member 37 and outer wall member 38 with respect tothe cusp 39. Accordingly, the inner wall member 37, or generallyspeaking the free movable member of gasket 36, is pressed against theinner wall of the stub of gas inlet opening 40. As long as gas flow ismaintained through the gas feed line 46, the gasket 36 seals the jointbetween the gas inlet opening 40 and the gas feed line 46. In addition,the gasket provides some clamping of the gas inlet opening 40 and thegas feed line 46 due to the pressure created by the purging gas.

In order to provide a seal between the gas inlet opening 40 and the gasfeed line 46, an elastic material can be used for the inner wall member.It is also conceivable to fabricate the entire gasket using an elasticmaterial such as rubber or the like. Alternatively, the gasket can beformed using a stiff material, e.g., a synthetic material, beingsubdivided into a plurality of fins which partially overlap each other.The fins are arranged such that the purge gas bends the fins along thecusp 39 in order to seal the joint between the gas inlet opening 40 andthe gas feed line 46.

It should be noted that a further gasket can be arranged in cases whenthe container 30 has a gas outlet through which the purge gas is removedby a gas discharge line. The further gasket is arranged between the gasoutlet opening and the gas discharge line and provides a similar asdescribed above a collapsible seal between the gas outlet opening andthe gas discharge line. In order to allow an unfolding by the passinggas stream, the cusp 39 joining the inner wall member 37 and the outerwall member 38 has to be oriented in the opposite direction so that thedischarged gas unfolds the sleeve formed by the inner wall member 37 andthe outer wall member 38. Accordingly, the gas outlet openingencapsulates the gas discharge line which can be arranged as a stub,similar to the embodiment of FIG. 7B.

In a further embodiment, sealing can be archived with a magneticenforced gasket. This could be archived with a metal or permanent magnetin the one interface side and electro magnet enforcement at other side(not shown in FIG. 7A or 7B).

According to the embodiments described with respect to FIGS. 7A and 7B,handling of photomasks with automated equipment is simplified. Forexample, a sensor at the shelf operated by a robot stops gas purging andinitiates gasket collapsing for placement and lifting of the container30.

This concept can be extended to the handling of wafer pods withinautomated stockers. There, container 30 carries a plurality ofsemi-conductor wafers instead of photomask 5. In a semi-conductormanufacturing unit, the wafer pods are frequently transported between ashelf and automatic processing units. Here, a sensor at the shelfoperated by a robot stops gas purging and initiates gasket collapsingfor placement and lifting of the container 30. At the processing units,a placement sensor will open the gas valve in order to expand thegasket. In case of purging the semiconductor wafer during processing orstorage, it is not necessary to interrupt the gas flow because there isno gas leakage and accordingly no human risk present.

The device described previously is able, by means of the purge device44, to effectively purge impurities within the container 30. On accountof relatively long periods of use, however, it can happen that crystalshave nevertheless formed on the transparent substrate 10 or thestructure elements 16. In order to be able to effectively remove them, adescription is given below of an activation of the crystals by means ofelectromagnetic radiation, which can be employed in addition to themeasures already mentioned.

As is shown in FIG. 8A, a microwave source 80 is used for this purposein a first aspect. The microwave source 80 emits microwave radiationhaving a specific wavelength and intensity. By way of example, anarrangement of two electrodes 84 connected to an RF generator 86 may beprovided for this purpose.

The microwave source 80 may for example also be integrated into theabove-described storage system 70 in accordance with FIG. 4 or bearranged in the vicinity of the holding frame 56 in accordance with FIG.4. Generally, the microwave source 80 may be arranged in the container30 or outside the container 30. The container 30 may also be a differentcontainer than for normal storage of the reticles, e.g., a microwave orinfrared oven, or be integrated into the exposure apparatus or a maskinspection apparatus.

In the case where the microwave source 80 is integrated into the storagesystem 70, the bottom flap 34 is open in this case in order to allow themicrowave radiation to impinge on the photomask 5 unimpeded. In thiscase, the microwave radiation irradiates the surface of the transparentsubstrate 10 and also the structure elements 16 thereof from the side ofthe protective film 20. The wavelength and/or intensity of the microwaveradiation of the microwave source 80 is chosen such that chemical bondsof deposits 24 on the surface of the transparent substrate 10 can breakup. It goes without saying that it is also possible to remove depositsin the volume 26 between the surface of the transparent substrate 10 andthe protective film 20 or on the surface of the protective film 20itself. The deposits 24 on the surface of the transparent substrate 10are usually disruptive for lithographic projection.

If the deposits comprise ammonium sulfate, the wavelength and/orintensity of the microwave radiation of the microwave source 80 shouldbe chosen such that hydrogen-oxygen bonds break up. This will beexplained in more detail again with reference to FIG. 9.

As is known, bonds within water or OH components are excited bymicrowave radiation, and they may break up in the process. Consequently,an equilibrium arises between the starting product (NH₄)₂SO₄ on the onehand, and the volatile constituents SO₃, NH₃ and H₂O, on the other hand,which equilibrium is shifted toward the volatile constituents in thecase of irradiation with microwaves. The formation of particles on thephotomask 5 is thus prevented as a result of the breaking up of the OHbonds 88 according to the structural formula of ammonium sulfate inaccordance with FIG. 9. It goes without saying that the procedurementioned can also be applied to other crystalline substances.

In this case, the volatile constituents are entrained by the purge gas,thereby preventing renewed crystallization. As is shown in FIG. 8A, thegas feed line 46 and the gas discharge line 48 are arranged in directproximity to the photomask 5 in order to remove the volatileconstituents. All the gases already mentioned above in the discussion ofthe embodiment in accordance with FIG. 3 are appropriate as the purgegas. In practice, the use of forming gas has proved to be particularlyeffective. As is known, forming gas is a hydrogen-nitrogen gas mixture,in which case the hydrogen proportion should be chosen to be below 5.7%here since gases comprising a higher proportion of hydrogen are highlyflammable.

The wavelength of the microwave radiation of the microwave source 80 maybe chosen such that it lies within a range in which the protective film20 is as transparent as possible to microwave radiation. In the case ofa protective film made of a Teflon-containing material, the transparentrange of the frequency of the microwave radiation lies between 2 GHz and3 GHz. Consequently, it is possible to use a conventional microwavesource having a frequency of the microwave radiation of approximately2455 MHz, such as is used e.g. in a microwave oven.

In order to bring the microwave radiation of the microwave source 80into the transparent range of the protective film 20, it is possible toprovide a filter 82 comprising, e.g., the material of the protectivefilm 20. Consequently, only radiation having a frequency at which theprotective film 20 is transparent advances as far as the photomask 5.

In a further embodiment, the microwave source 80 may also be pulsed inorder as far as possible to prevent electrostatic charging orspark-overs on electrically conductive structure elements on thetransparent substrate. Likewise, the microwave radiation should notdamage adhesives for the fixing of the frame 18 or the protective film20.

As is shown in FIG. 8B, an infrared source 90 is provided in a secondaspect. The infrared source 90 emits infrared radiation having aspecific wavelength and intensity onto the surface of the transparentsubstrate from the side of the protective film. By way of example, amirror 94 may also be used for deflection onto the transparent substrate10. The infrared source 90 may likewise be integrated into theabove-described storage system 70 in accordance with FIG. 4 or bearranged in the vicinity of the holding frame 56 in accordance with FIG.4. The bottom flap 34 is advantageously open in this case in order topermit the infrared radiation to impinge on the photomask 5 unimpeded.In this case, the infrared radiation irradiates the surface of thetransparent substrate 10 and also the structure elements 16 thereof fromthe side of the protective film 20.

The infrared source 90 heats crystalline deposits on the surface of thetransparent substrate in order that their volatile constituents aresubsequently removed by means of the purge gas. In this case, the gasfeed line 46 and the gas discharge line 48 are once again arranged indirect proximity to the photomask 5 in order to remove the volatileconstituents.

The wavelength of the infrared radiation of the infrared source 90 isonce again chosen such that it lies within a range in which theprotective film 20 is at least partly transparent to infrared radiation,but the impurities are activated to a sufficient extent. Thisnecessitates, on the one hand, a high transmission for infraredradiation in the protective film 20 and a high absorption for infraredradiation of the impurities.

A useable frequency range is explained below with reference to FIGS. 10and 11.

FIG. 10 shows an absorption spectrum for ammonium sulfate. A pluralityof absorption edges which can be used for the method according to theinvention lie within the range of a wave number of the infraredradiation of between 1000 cm⁻¹ and 4000 cm⁻¹. Thus the wave number ofthe infrared radiation could lie within the range of between 1100 cm⁻¹and 1400 cm⁻¹ or 2500 cm⁻¹ and 3500 cm⁻¹.

FIG. 11 shows a transmission spectrum for a fluoropolymer which is acustomary material for the production of protective films 20. It isevident that the material of the protective film 20 is sufficientlytransparent in the abovementioned ranges. The transmission values of theprotective film 20 are for the most part above about 90%.

According to the invention, impurities directly in the vicinity of thephotomask are removed by means of purge gases, thereby suppressingcrystal growth on the surface of the photomask. Accordingly, the timebetween photomask cleaning steps can be significantly lengthened.

Having described embodiments for a device for the storage and use of atleast one photomask for lithographic projection and a method for usingthe device in a fabrication installation and non-volatile memory cells,it is noted that modifications and variations can be made by personsskilled in the art in light of the above teachings. It is therefore tobe understood that changes may be made in the particular embodiments ofthe invention disclosed which are within the scope and spirit of theinvention as defined by the appended claims.

Having thus described the invention with the details and theparticularity required by the patent laws, what is claimed and desiredto be protected by Letters Patent is set forth in the appended claims.

1. A device for storage and use of at least one photomask forlithographic projection, the device comprising: a container suitable forreceiving a photomask, the container comprising a container housing anda closable opening device situated at the container housing and servingfor the entry and issuing of the photomask, the container comprising atleast one gas inlet opening arranged in such a way that, in the case ofpurging the photomask, a purge gas flushes around the photomask with asubstantially laminar flow.
 2. The device according to claim 1, whereinthe photomask comprises a transparent substrate, which is provided witha pattern of absorbent, partly absorbent, phase-shifting or reflectivestructure elements on its front side, and comprising a frame, which isarranged on the front side of the transparent substrate outside thepattern of absorbent, partly absorbent or phase-shifting structureelements, and comprises a protective film, which is arranged above thetransparent substrate on the frame in order to protect the structureelements from particles in an at least partly closed-off volume.
 3. Thedevice according to claim 2, wherein the protective film is permeable togaseous substances of the purge gas toward the volume.
 4. The deviceaccording to claim 2, wherein the protective film is provided with onepinhole or a plurality of pinholes in order to enable a gas exchangebetween the volume and the region outside the volume.
 5. The deviceaccording to claim 2, wherein the frame is provided with one pinhole ora plurality of pinholes in order to enable a gas exchange between thevolume and the region outside the volume.
 6. The device according toclaim 1, wherein the container housing comprises an electrostaticallydissipating coating.
 7. The device according to claim 1, wherein thecontainer housing comprises a reticle holder in order to hold thephotomask in a predetermined position.
 8. Device according to claim 7,wherein the closable opening is a bottom flap and comprises a reticlesupport in order to hold the photomask in a predetermined position. 9.The device according to claim 8, wherein the gas inlet opening and thegas outlet opening are arranged on the bottom flap in a manner offsetwith respect to the photomask.
 10. The device according to claim 1,wherein the container comprises a handling flange suitable fortransferring the photomask to an exposure apparatus by means of amechanical interface.
 11. The device according to claim 1, wherein thecontainer and the bottom flap correspond to an industry standardaccording to a SEMI standard.
 12. The device according to claim 11,wherein the mechanical interface corresponds to an industry standardaccording to a SEMI standard.
 13. A device for storage and use of atleast one photomask for lithographic projection, the device comprising:a container suitable for receiving a photomask, the container comprisinga container housing and a closable opening device situated at thecontainer housing and serving for the entry and issuing of thephotomask, the container comprising at least one gas inlet openingarranged in such a way that, in the case of purging the photomask, apurge gas flushes around the photomask; and a purge device comprising atleast one gas feed line connected to the gas inlet opening, the purgedevice being suitable for purging the container with a purge gas inorder to prevent crystallization on the photomask, and in which thecontainer comprises a gas outlet opening and the purge devicefurthermore comprises at least one gas discharge line connected to thegas outlet opening.
 14. The device according to claim 13, wherein thepurging device is connected to an adapter plate arranged below thebottom flap of the container, so that the gas feed line is connected tothe gas inlet opening and the gas discharge line is connected to the gasoutlet opening.
 15. The device according to claim 14, further comprisinga holding frame suitable for receiving the container, said holding framecomprises fixings suitable for receiving the adapter plate.
 16. Thedevice according to claim 15, wherein the fixings are embodied inscrewable fashion in order to enable the adapter plate to be exchanged.17. The device according to claim 14, wherein the adapter plate isembodied in the holding frame as rack bottom on which the container withthe photomask is placed and can be secured by means of a hingedmechanism.
 18. The device according to claim 14, wherein the positioningof the container in the holding frame is effected by means of thehandling flange.
 19. The device according to claim 14, wherein thepositioning of the photomask in the container is effected by means ofconstant contact pressure.
 20. The device according to claim 17, whereinthe hinged mechanism is embodied in the form of a clip, which is fittedto the holding frame in a rotatable manner and can be pivoted into areceiving position and a holding position.
 21. A device for storage anduse of at least one photomask for lithographic projection, the devicecomprising: a container suitable for receiving a photomask, thecontainer comprising a container housing and a closable opening devicesituated at the container housing and serving for the entry and issuingof the photomask, the container comprising at least one gas inletopening arranged in such a way that, in the case of purging thephotomask, a purge gas flushes around the photomask with a substantiallylaminar flow; and a purge device comprising at least one gas feed lineconnected to the gas inlet opening, the purge device being suitable forpurging the container with a purge gas in order to preventcrystallization on the photomask, and in which the container comprises agas outlet opening and the purge device furthermore comprises at leastone gas discharge line connected to the gas outlet opening, said purgingdevice being arranged below the bottom flap of the container, so thatthe gas feed line is connected to the gas inlet opening and the gasdischarge line is connected to the gas outlet opening.
 22. The deviceaccording to claim 21, wherein the purge device comprises a mixingdevice for purging with a plurality of gases, the mixing devicecomprising a T-piece and mixing valve in order to admix the plurality ofgases in the desired mixing ratio.
 23. The device according to claim 22,wherein the purge device feeds a gas mixture for cleaning of organiccontaminations as purge gas.
 24. The device according to claim 23,wherein the purge device feeds a nitrogen-ozone gas mixture.
 25. Thedevice according to claim 22, wherein the purge device feeds a gasmixture for cleaning of inorganic contaminations as purge gas.
 26. Thedevice according to claim 25, wherein the purge device feeds anitrogen-argon gas mixture.
 27. The device according to claim 22,wherein the purge device feeds a nitrogen-hydrogen gas mixture.
 28. Thedevice according to claim 27, wherein the purge device feeds ahydrogen-containing gas mixture.
 29. The device according to claim 28,wherein the gas mixture is a forming gas in which the hydrogenproportion is chosen below a flammability threshold.
 30. The deviceaccording to claim 22, wherein the purge device feeds a nitrogen-carbondioxide gas mixture.
 31. The device according to claim 21, wherein thepurge device controls the gas temperature and/or the gas partialpressures of the purge gas alongside the mixing ratios.
 32. The deviceaccording to claim 21, wherein the purge device feeds a gas mixturesuitable for removing water from the surface of the photomask.
 33. Thedevice according to claim 32, wherein the purge device feeds anitrogen-oxygen gas mixture.
 34. The device according to claim 32,wherein the purge device feeds an air mixture from which water comprisesbeen removed.
 35. A device for storage and use of at least one photomaskfor lithographic projection, the device comprising: a container suitablefor receiving a photomask, the container comprising a container housingand a closable opening device situated at the container housing andserving for the entry and issuing of the photomask, the containercomprising at least one gas inlet opening arranged in such a way that,in the case of purging the photomask, a purge gas flushes around thephotomask with a substantially laminar flow; and a microwave sourcesuitable for emitting microwave radiation comprising a specificwavelength and intensity from the side of the structure elements ontothe photomask.
 36. The device according to claim 35, wherein thewavelength and/or intensity of the microwave radiation of the microwavesource is chosen such that chemical bonds of impurities on the surfaceof the transparent substrate, in the volume between the surface of thetransparent substrate and the protective film or on the surface of theprotective film at least partly break up.
 37. The device according toclaim 36, wherein the wavelength and/or intensity of the microwaveradiation of the microwave source is furthermore chosen such thathydrogen-oxygen bonds in the impurities at least partly break up. 38.The device according to claim 37, wherein the impurities compriseammonium sulfate present in crystalline form on the surface of thetransparent substrate, in the volume between the surface of thetransparent substrate and the protective film or on the surface of theprotective film.
 39. The device according to claim 35, wherein thewavelength of the microwave radiation of the microwave source isfurthermore chosen such that it lies within a range in which theprotective film is at least partly transparent to microwave radiation.40. The device according to claim 39, wherein the protective filmcomprises a Teflon-containing material.
 41. The device according toclaim 39, wherein the frequency of the microwave radiation lies withinthe range of between 2 GHz and 3 GHz.
 42. The device according to claim41, wherein the frequency of the microwave radiation is approximately2455 MHz.
 43. The device according to claim 35, wherein the wavelengthand intensity of the microwave radiation of the microwave source arefurthermore chosen such that no or virtually no electrostatic chargingor spark-overs occur on electrically conductive structure elements onthe transparent substrate.
 44. The device according to claim 43, whereinthe microwave source is pulsed.
 45. The device according to claim 35,wherein the wavelength and intensity of the microwave radiation isfurthermore chosen such that water at least partly absorbs the microwaveradiation.
 46. The device according to claim 35, wherein the photomaskcomprises a frame, the protective film of the photomask is fixed to theframe by means of an adhesive, and the wavelength and intensity of themicrowave radiation is furthermore chosen such that the microwaveradiation does not damage the adhesive.
 47. The device according toclaim 35, wherein the microwave source comprises a filter comprising thematerial of the protective film.
 48. A device for storage and use of atleast one photomask for lithographic projection, the device comprising:a container suitable for receiving a photomask, the container comprisinga container housing and a closable opening device situated at thecontainer housing and serving for the entry and issuing of thephotomask, the container comprising at least one gas inlet openingarranged in such a way that, in the case of purging the photomask, apurge gas flushes around the photomask with a substantially laminarflow; and an infrared source suitable for emitting infrared radiationcomprising a specific wavelength and intensity from the side of thestructure elements onto the photomask.
 49. The device according to claim48, wherein the wavelength and/or intensity of the infrared radiation ofthe infrared source is suitable for heating impurities on the surface ofthe transparent substrate, in the volume between the surface of thetransparent substrate and the protective film or on the surface of theprotective film.
 50. The device according to claim 48, wherein thewavelength of the infrared radiation of the infrared source isfurthermore chosen such that it lies within a range in which theprotective film is at least partly transparent to infrared radiation.51. The device according to claim 48, wherein the wavenumber of theinfrared radiation lies within the range of between 1000 cm⁻¹ and 4000cm⁻¹.
 52. The device according to claim 51, wherein the wavenumber ofthe infrared radiation lies within the range of between 1100 cm⁻¹ and1400 cm⁻¹.
 53. The device according to claim 51, wherein the wavenumberof the infrared radiation lies within the range of between 2500 cm⁻¹ and3500 cm⁻¹.
 54. The device according to claim 48, wherein the intensityof the infrared radiation is chosen such that the infrared radiationheats ammonium sulfate.
 55. The device according to claim 48, furthercomprising a mirror that directs the infrared radiation of the infraredsource onto the photomask.
 56. A device for storage and use of at leastone photomask for lithographic projection, the device comprising: acontainer suitable for receiving a photomask, the container comprising acontainer housing and a closable opening device situated at thecontainer housing and serving for the entry and issuing of thephotomask, the container comprising at least one gas inlet openingarranged in such a way that, in the case of purging the photomask, apurge gas flushes around the photomask through a gas feed line; and agasket being arranged between said one gas inlet opening and said gasfeed line, said gasket providing a collapsible seal between said gasinlet opening and said gas feed line.
 57. The device according to claim56, wherein said container further comprises at least one gas outletopening arranged in such a way that, in the case of purging thephotomask, the purge gas is removed through a gas discharge line and afurther gasket being arranged between said one gas outlet opening andsaid gas discharge line, said further gasket providing a collapsibleseal between said gas outlet opening and said gas discharge line. 58.The device according to claim 57, wherein the gasket and/or the furthergasket are formed from a self-inflating material.
 59. The deviceaccording to claim 58, wherein the gasket is arranged in a toroidalshape between the gas inlet opening 40 and the gas feed line.
 60. Thedevice according to claim 58, wherein the gasket is provided as acollapsible gasket having a passive state of being collapsed.
 61. Thedevice according to claim 58, wherein the gasket is provided as acollapsible gasket having a passive state of being expanded.
 62. Thedevice according to claim 57, wherein the gas inlet opening is arrangedas a stub and the gas feed line is adapted to house the gas inletopening in an overlapping manner.
 63. The device according to claim 62,wherein the gas discharge line is arranged as a stub and the gas outletopening is adapted to house the gas discharge line in an overlappingmanner.
 64. The device according to claim 62, wherein the gasket and/orthe further gasket are arranged as a sleeve having a double-walledcross-section.
 65. The device according to claim 64, wherein the sleevecomprises an outer wall member and an inner wall member which arearranged such that a passing gas stream unfolds the inner wall memberand the out wall member to provide the collapsible seal.
 66. The deviceaccording to claim 65, wherein said outer wall member or said inner wallmember comprise an elastic material.
 67. The device according to claim66, wherein said outer wall member and said inner wall member beingsubdivided into a plurality of fins which partially overlap each other.68. The device according to claim 67, wherein said fins are arrangedsuch that the purge gas bends the fins in order to provide thecollapsible seal.
 69. A device for storage and use of a work piece insemiconductor manufacturing, the device comprising: a container suitablefor receiving the work piece, the container comprising a containerhousing and a closable opening device situated at the container housingand serving for the entry and issuing of the work piece, the containercomprising at least one gas inlet opening arranged in such a way that,in the case of purging the work piece, a purge gas flushes around thework piece through a gas feed line; and a gasket being arranged betweensaid one gas inlet opening and said gas feed line, said gasket providinga collapsible seal between said gas inlet opening and said gas feedline.
 70. The device according to claim 69, wherein said work piececomprises a plurality of semiconductor wafers.
 71. The device accordingto claim 69, wherein said work piece comprises a photo mask.
 72. Amethod for using a device in a fabrication installation, the methodcomprising: providing a fabrication installation comprising at least oneexposure apparatus suitable for receiving the photomask; feeding thephotomask from the container into the exposure apparatus; carrying outone or more exposure processes with the exposure apparatus using lightfrom a UV source; removing the photomask from the exposure apparatusinto the container; and cleaning the photomask in the container bypurging with the purge gas.
 73. The method according to claim 72,further comprising: providing the microwave source; irradiating thephotomask with microwave radiation; and cleaning the photomask in thecontainer by purging with the purge gas.
 74. The method according toclaim 72, further comprising: providing the infrared source; irradiatingthe photomask with microwave radiation; and cleaning the photomask inthe container by purging with the purge gas.